Torque transmitters of the prior art have relied mainly on frictional coefficients for their operation. Whether the transmitters use frictional surfaces or plates, the frictional coefficients vary significantly with ambient conditions such as humidity and thus are imprecise or cannot be accurately calibrated to make certain that a predetermined torque is applied but not exceeded. The problem is accentuated in space due to the lack of oxygen, frictional coefficients may vary as much as 50% from their value on Earth.
U.S. Pat. No. 3,707,888 to Schottler discloses a variable speed transmission for transmitting torque to an output shaft at a substantially constant selected speed. Driving balls arranged in constant rolling frictional contact with pairs of inner and outer concentric and axially separate ball races. One pair of races is associated with an input shaft, and the other pair of races is associated with the output shaft. The driving balls and races engage along contact tracks defined on the races and balls to thereby transmit torque between the shafts at a speed ratio determined by the contact tracks. Control means adjusts the axial positioning of one pair of races within a selected range to infinitely vary the contact tracks and thereby vary the speed ratio. Pressure regulator means responds to differential twist torque between the shafts to maintain the balls and races in frictional rolling contact throughout said selected range of adjustment and vary the contact pressure between races and balls in proportion to the output torque.
U.S. Pat. No. 3,991,592 to Brems et al discloses a safety overload clutch wherein the driving and driven members are retained in driving relation by a primary roller on one of the members which is urged radially into a groove on the other member by an elastic flexible ring loaded by one or more secondary rollers on the one member positioned substantially diametrically opposite the primary roller. When the load on the driven member exceeds a predetermined value, the primary roller rolls out of its groove causing additional deflection of the flexure ring.
U.S. Pat. No. 4,667,525 to Schottler discloses variable speed frictional transmissions that basically depend on driving balls arranged in constant rolling frictional contact with a pair of inner and a pair of outer concentric and axially separable ball races are improved by the provision of (1) new speed control units for changing the relative positions of balls and races to produce desired speed changes and (2) new cam and roller units for maintaining the balls and races in forced contact even when the transmissions are under no-load conditions. The new transmissions are characterized by (A) outer and inner circular concave race tracks and (B) a simplified hydraulic feed-back control mechanism which displaces the outer control race only in the direction of speed increase, while its opposite displacement is actuated by torque forces plus spring pressure. In contrast to prior devices of their class, it is further disclosed that the transmissions (a) do not produce any gyratory forces at any speed of operation, (b) do not increase input torque requirements as output speed is decreased, (c) do not have parts that may get out of phase when the transmissions are under no-load condition and (d) have greater power capacity per unit size.
U.S. Pat. No. 4,926,715 to Hirt et al discloses a planetary gear train comprising at least two planetary gear sets arranged coaxially behind, and drivingly connected with, one another, of which one planetary gear set contains fewer, and the other planetary set more, planet gears and the planet gears and their bearings in both planetary gear sets are identically constructed.